It is known, as shown in the prior art configuration of FIG. 1, to electrically charge and discharge an electrical load (1) used in a hybrid electric vehicle (HEV) or electric vehicle (EV) (not shown). The electrical load (1) is pre-charged to a predetermined voltage value before a steady-state high current is applied to the load (1). A first, or positive contactor device (2), a second, or negative contactor device (3), and a third contactor device (4) are operatively controlled with a controller (5) to provide the pre-charge predetermined voltage value to the electrical load (1). Contacting devices (2, 3) are defined as a device being electrically rated for operation at a typical voltage rating of 300-400 volts DC or higher and a typical continuous current rating of several hundred of amps DC or more. Contacting device (4) has a similar voltage rating as contacting devices (2,3), but a typical lower continuous direct current (DC) current rating in the 10 to 20 amp range. Contacting devices (2, 3) generally have a package size that has a typical height of 10 centimeters and a diameter of about 7 centimeters. Contacting device (4) has a typical height of 5 centimeters, a typical length of 4 centimeters, and a typical width 3.5 centimeters. Contactor devices are used because of their known electrical circuit isolation properties. For example, a typical contactor device may have an isolation resistance of greater than 500 ohms/volt. Pre-charging the load to the predetermined voltage value before the steady-state high current is applied to the electrical load is desired so as to limit the in-rush current through the positive and the negative contactor at contact make and to limit the electrical energy applied to the electrical load. A battery (6) is electrically connected with the electrical load (1) through the contactor devices, or relays (2, 3, 4). Relays (2, 3, 4) are make/break relays which may be defined as contact closure that completes the electrical circuit where current flows through the respective relay and break is the opening of the circuit where current does not flow through the relay. It is desired to pre-charge the electrical load through the third contactor device such that closure of the first and second contactor devices into the electrical load to not have a large electrical potential. Closing the first and second contactor device into an electrical load having a large electrical potential may cause undesired damage or reduced service life to the contactor. Similarly, interruption or breaking of the electrical circuit by the contactor under large, or heavy electrical load may also result in the undesired consequence of reduced service life of the contactor.
A current-limiting resistor (7) is connected in series electrical connection with the third contactor relay (4). The current-limiting resistor (7) is used to limit the applied current from the battery (6) through the third contactor relay (4) to attain a certain pre-charge voltage value at the electrical load (1). The electrical load (1) may also be electrically unconnected from the battery with operative control of the contactor relays (2, 3, 4) to prevent current from being applied to electrical load (1).
The third contactor relay (4) that supplies the voltage of the battery (6) to the electrical load (1) has an undesired large size, weight, and cost. The current-limiting resistor (7) has an undesired large size and weight and also radiates undesired heat in relation to the voltage applied thereacross. The physical size of a current-limiting resistor is typically 12 centimeters in length with a height of about 2 centimeters. The resistance value of the current-limiting resister determines the pre-charge voltage value realized at the electrical load (1) with little flexibility to attain different, other pre-charge voltage values.
It is desired to provide a robust, reliable power charging assembly that is configured to provide a pre-charge state, a steady-state, high-current state, and an unconnect state for an electrical load while decreasing the size, weight, parts count, and cost of the corresponding electrical components that make up the power charging assembly. Providing flexibility to attain one of a plurality of values for the pre-charge value of the electrical load is also desired.